1. Field of the Invention
The invention relates generally to releasable wellbore packers. In particular aspects, the invention relates to improved packer devices and methods for release of packer devices from a wellbore.
2. Description of the Related Art
Packers are set within a wellbore to form a fluid seal between the borehole wall and a tubing string. Non-retrievable, or permanent, packers are sometimes used where a permanent closure is desired. In order to remove a permanent packer, a milling tool is disposed into the wellbore above the packer and mill away the upper setting slips that hold the packer in its set position. This process is time consuming and requires an additional trip into the well. In other cases, retrievable packers are used, which allow the option to release the packer from its set position and removing it.
A standard technique for removing retrievable packers involves pulling upwardly to shear a shear ring or other shearable member. U.S. Pat. No. 4,688,641 issued to Knierieman, for example, discloses a well packer that is releasable by use of a jarring tool that shears a threaded connection, there by releasing the packer from its set position. Shear members of a predetermined load are often used where the upward loading on the packer can be limited during normal production and standard well conditions. However, this is not always the case, and an alternative arrangement is needed.
U.S. Pat. No. 3,990,510 describes a well anchor tool that uses a set of releasable collet fingers to set the packer element. A special retrieving tool, which is run into the wellbore separately, can engage the collet fingers and release them to unset the packer.
Other retrievable packer designs are known, but these suffer from similar drawbacks. Retrievable packers generally do not provide for a means of hydraulically releasing the packer assembly from the wellbore.
The present invention addresses the problems of the prior art.